Angular velocity responsive apparatus



July 4, 1950 J. I YMAN ANGULAR vELoci'rY RESPONSIVE APPARATUS 2Sheets-Sheet 1 Filed Oct. 17, 1945 WN uvm.

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mw uw bw AlNvEmoR dosi/2H L Y/v//y/v Y j Al w/fl f l go Nev July 4, 195oFiled Oct. 17, 1945 J. LYMAN ANGULAR VELOCITY RESPONSIVE APPARATUS 2Sheets-Sheet 2 INVENTOR JOSE/DH Y ,QN

JMYM@ Patented July 4, 1950 ANGULAR VELOCITY RESPONSIVE APPARATUS JosephLyman, Huntington, N. Y., assigner to The Sperry Corporation, acorporation of Dela- Application october 17, 1945, serai No. 622,739 lclaims. (o1. 264-1) The present invention relates to orientationresponsive apparatus, and more particularlyto r an improved instrumentfor indicating changes of orientation.

A further object of the present invention is to provide an improvedinstrument for detecting the rate of turn or change of orientation oI- abody, or forV detecting both angular velocity and angular accelerationof a body.

In accordance with the present invention, a m'ass is elasticallysupported by a base and is arranged so that its moment of inertiarelative to a 'selectedaxis is periodically varied. Upon rotation of thebase, the mass is constrained by its elastic connection to rotate alongwith the base, but its inertia compels it to lag slightly behind thebase 4in rotation about the selected axis, byg

an average angle of displacement substantially proportional to theangular acceleration of the base. Moreover, since the moment of inertiaof the mass about the selected axis is alternately increasing anddecreasing periodically, the relative angular displacement between thebase and the mass varies periodically and synchronously with thevariation of the moment of inertia of the mass. The amplitude of theperiodic variation of angular displacement between the mass and the baseis substantially .proportional to the rate of change of orientation ofthe base about the selected axis, i. e., substantially proportional tothe angular velocity of the base. An example of such a mass is a leafspring clamped at one end, and

present invention. a phase-sensitive detector system and a torsionalvibration pickup device may be employed in conjunction with the tunedfork and the base for detecting or for indicating the relative phase andamplitude of torsional vibrations or periodic variations 4of angulardisplacement between the fork and the base, and thus for determining theangular velocity of the base about the .selected axis.

The invention in another of its aspects relates to novel features of theinstrumentalities described herein for achieving the principal objectsof the invention and to novel principles employed in thoseinstrumentalities, whether or not these features and` principles areused for the said principal objects or in the said neld.'

A further object of the invention is to provide improved apparatus andinstrumentalities embodying novel features and principles, adapted for,use in realizing the above objects and also adapted for use in otheriields.

An embodiment of the present invention will now be described withreference to the accompanying drawings, wherein:

Fig. 1 is a, schematic diagram of an embodiment of the presentinvention;

Fig. 2 is a front elevation, partly in section, of aY tuned forkassembly with an exciter unit and vibration pickup devices;

Fig. 3 is a side elevation, partly in section, of the assembly shown inFig. 2; and Y Fig. 4 is a. cross-sectional view taken along the line 4-4 'in Fig. 3.

Referring now particularly to Fig. 1, there is shown a tuned fork IIconnected by an elastic constraining portion I2 to a base I3.

preferably weighted at the other, so that it is v forced to turn withthe body about the major axis of the spring or an axis parallelthereto,.but may vibrate like one tine of a tuning fork across saidaxis.

According to a further feature of the present invention, the mass maycomprise two bodies elastically connected to the base and symmetricallydisposed about the selected axis, and arranged so that the bodies movealternately toward and away from each other, so that the moment ofinertia of the symmetrical mass about the selected axis may be variedwith minimum reaction coupling to the base. The two massive bodies maycomprise the tines of a tuned fork, which may be elastically coupled tothe base at the junction of the two tines.

In accordance with still 'further features of the The fork I I comprisestwo tines I4 and. I5 of substantially equal size and weight, the twotines being arranged for vibration in their plane, alternately towardand apart from each other, and being resonant at a .predeterminedfundamental frequency of vibration.

A pair of vibrational pickup devices I6 and Il is attached tothe tinesI4 and I5 near thejunction of the tines with the elasticconstrainingportion I'2. These pickup devices, which may take i the formof Rochelle salt crystal pickup devices, are employed for producing analternating voltage corresponding to the wave form of vibration of thetines I4 and I5.

The pickup devices I6 and I'I are connected in series, and are connectedto the input circuit of an ampliner I8, whose output circuit may beconnected either directly or through afrectifler I9 lto anelectromagnetic tuned fork exciter 'arrangement 2i. -The electromagneticexciter arrangement may comprise either a pair of coils having theiraxes substantially aligned with the tines I4 and I5, or it may comprisea single coil symmetrically disposed betweeen the tines I4 and I5 andhaving its axis aligned for perpendicular intertion with theelectromagnetic exciter arrange-- ment 2| depends upon the nature of theelectromagnetic exciter arrangement. coils are so designed that theycompel the tines I4 and I5 to move toward each other on both positivepeaks and negative peaks of the output voltage of ampliner I3, then therectiiier I9 should be employed. On the other hand, if the one polarity,then the rectifier i9 is obviated. An arrangement of parallel excitercoilsv 46, 41 having permanently magnetized Alnico cores 48,

49 has been vfound to operate satisfactorily for.

If the exciter arranged to receive the bottom portion of the crystalpickup unit 23. The connection of the upper portion of the crystalpickup unit 23 through the rigid rod 25 is clearly shown in Fig. 2. Therod 25 extends along the axis of symmetry 24 of the fork II through aconformal cylindrical opening at the junction of the tines I4 and I5,and a set screw 44 is provided for clamping the rod 25 to the fork II ina stressgeg condition after the system has been assem- The exciter unit2l. illustrated in Figs. 2 and 3, comprises a pair of coils 46 and 41cooperating with core rods 48 and 43. These rods are secured in a brasstop plate 5I which cooperates with the cylindrical housing II) tocomplete the enclosure of the fork il and the pickup units associated fmagnetic design factorsvof the exciter arrangei ment 2| are such thattines I4 and I5 are drawn together only during amplier output peaksl oisustaining vibration ofthe tines I4 and I5 at the frequency of theampliner output voltage without the necessity of a rectifier I3.

-A further or torsional vibration pickup 231s arranged for producing anoutput voltage corresponding t0 relative angular displacement ortorsional vibration between the tuned fork il and the base I3, about theaxis of symmetry 24 of the tunedfork Il.

The torsion pickup 23 has a stator portion rigidly connected to the baseI3, and it has a relatively movable portion connected through a stiftrod 25 toA the tuned fork II. For this purpose, the rod r The pickupdevice 23 may` comprise still another Rochelle salt 4crystal unit.

25 passes along the axis 24 in spaced relation to the base I3 and to theelastic constraining portion I2 and it is rigidly connected to the forkII at the junction of the tines I 4 and I5.

. tubular housing I0 may be made of brass, for example. A brass block 4Iis fastened in position as shown within the tubular'housng I0, and

; is employed'for supporting the fork II through the elastic torsionalconstraining portion I2.

therewith. The lower ends of the core members 48 and 49 .are so situatedthat a very small spacing is provided between these ends and the endsofthe tines I4 and I5, respectively, so that an emcient magneticexcitation circuit isprovided.

fIt .is important for precise operation of the structure illustrated inthe Figs. 2, 3 and 4, if the, turn-responsive apparatus is designed forhigh sensitivity, `that the mass in the fork Il be perfectly symmetricalabout the. axis of the rod 25 and the apparent axis of symmetry 24 ofthe fork II. To aid -in securing the desired accurate distribution oimass of the assembly, one or more adjustably positioned mass units maybe attached to the fork II. Two adjustable mass units 52 and 53 areshown positioned on mass adjustment screws 54 and 55, for aid inbalancing the system illustrated in Figs. 2, 3 and 4 and in tuning, thenatural period of torsional oscillation to match the tuning forkfrequency.

It will .be readily apparent that the elastic constraining section I2through which the fork II is secured to the base I3 could take any of awide variety of forms. For high sensitivity of the system. 'it isdesirable that the torsional stillness of this constraining section besmall, in order that appreciable deection of the fork about its axis 24will result from the application of a small torque. At the same time, itis desirable that the constraining section I2 have high stiffnessrelative to ybending forces, inlorderto'retain the axis ofthe fork IIaligned with the axis of the cylin- 'fdri'cahhousing I0. Forthisipurpose, the con- ."sti'aining .section I2 may be made in the formillustrated in Figs. 2 and- 3, the cross-sectional Pickup devices I8 andI1 are mounted at the the elastic constraining member I2. The movl andI1 are coupled to the tines I4 and I5 a, shortr Y.

distance above the junction of the tines. As illusform being as shown inFig. 4.

Returning again to Fig. 1, there'are shown circuits Aafllcl apparatus inconjunction with the fork .II and vibration sustainingsystem I6, Il, I8,I9,

2i; for: providing a measureof the angular velocity and a measure of theangular acceleration of thejbase I3.: about the axis l24 .of the forkII.

-l-.fTlie` electric output circuit of `the angular displacement pickup,device 23 is connected to the .l inputlcircuit of an amplifier 26,whose output trated in Figs.' 2 and 3, the cross-sectional dimensionsofthe-tines I4 and I5 may be varied along i their length 'forcontrolling the vibrational characteristicsof the-fork II as desired.

The crystal pickup unit 23 for producing an Q output voltage varying asthe relative angular or torsional displacement between the fork I I andthe base I3 may be rigidly connected to the 'base'.

which may .be attached, in turn, to the block 4|.

made of Bakelite, for example, is fastened in the An insulated bottomportion 43, which may be 2l requires 4a. reference phase input signal,so .bottom ofthe inner housing member 42 and is 71| that. the outputvoltage will be compelled to vary circuit,- is connected to thelsignalinput circuit of .a phase-sensitive detector 21, which may be of thewell-known balanced modulator type.

.'inputlsignal amplitude. This direct output voltage mayjb'e supplied toa galvanometer 28 emfpl'oyed as a rate-of-turn indicator.

A s is well known, the phase-sensitive detector in polarity according torelative changes of input signal phase. For this purpose, the outputvoltage of pickup units I6 and I1 may be applied to the input circuit ofan amplifier 29, whose output-circuit is connected to the phasereferenceinput terminals of the phase-sensitive detector 21.

While the base I3 of the apparatus shown in Fig. 1 remains in fixedorientation, no torque is applied to the elastic constraining sectionI2, and the tuned fork II therefore remains in neutral angularpositional relation to the base I3 with respect to the axis 24 of thetuned fork II. During rotation of the base I3 about the axis 24, on theothery hand, the elastic constraining section I2 connecting the fork IIto the base I3 compels the fork II to turn substantially with the baseI3. Since the fork II has appreciable inertia, its moment of inertiaabout the axis 24 being determined principally by the mass of the tinesI4 and I5 and the spacing of these tines from .the axis 24, and sincethe torsional constraining section I2 has torsional elasticity, therotation of the base I3 about the laxis 24 is accompanied by sometorsional de- KAtions "between the fork II and the base I3 arevconsistent with the law of conservation of angular momentum. If thebase is rotating at constant speed, it will be necessary that the speedof rotation of the fork, increase as its moment of inertia about theaxis of rotation decreases, and decrease as the moment of inertiaincreases, all in synchronism with the fork oscillations, in itstendency to satisfy the condition of substantially constant angularmomentum.

The axial pickup device 23 produces an alternating voltagecorresponding4 to Ithis periodic variation of angular displacement.'Ihis alternating voltage is of the same frequency as that of the forkand varies in magnitude and in phase relation to the phase of the output,voltage of pickup devices I6 and I1, according to the rate of rotationof base I3 about Iaxis '.24 and the direction or sense of the rotation.Accordingly, the phase-sensitive detector 21 is enabled to provide anoutput signal which-unambiguously indicates the character of the changeof orientation of the base I3. j

In order that the` deflectiom-if` the point 3| of the rate-of-turnindicator 23 b e made-to vary in a predetermined relation to therate ofchange of orientation of the base I3, it is necessary that the amplitudeof the periodic 4change in the moment of inertia of the fork I I bemaintained substantially constant. Thus, `it necessary that thevibration of the tines I4 and be accuratelyA regulated to asubstantially constant amplitude. For this purpose, an automaticgaincontrol circuit is employed in conjunction with the vibrationsustaining amplifier I8. The output voltage of amplifier 29 is rectifiedand applied to the automatic gain-control terminals of the amplifier I8.

The rectifier unit 32 receives from amplifier 29 an alternating voltageof amplitude proportional to the amplitude of vibration of the tines I4and I5, and supplies a proportionate rectiiied voltage to thegain-control terminals of amplifier I8. The direct voltage supplied bythe rectlfler may be employed for bias potential variation of avariable-mu amplifier in a well-known manner, or may be used forautomatic gain control in any desired arrangement of amplifier I3.

During a uniform angular acceleration of the base I3 about the axis 24,the amplitude of the alternating component of output voltage from pickup'device 23 increases steadily and, in addition, a unidirectional voltagecomponent is produced by the device 23 corresponding to the angularacceleration of the base I3. During an angular deceleration of thebaseI3, an opposite direct voltage is produced by the pickup device 23. Thedirect voltage output of pickup device 23 represents an accurate measureof the angular acceleration of the base I3 about axis 24. Accordingly, adirect-current amplifier 33, which may be of the direct-coupled type,may be connected to the pickup device 23 to receive and amplify thedirect or unidirectional component of voltage produced thereby; and theoutput ofV the amplifier may be connected to a galvanometer -34 employedas an acceleration indicator. If a piezoelectric crystal device isemployed as the pickup unit 23, the input impedance of thedirect-current amplifier 33 should be very high, in order that prolongedaccelerations may be registered by the acceleration indicator 34.

It will be seen from theforegoing remarks that the present invention isfundamentally ideally adapted both for use as an accurate. rugged andreliable rate-of-turn indicator and for use as an angular accelerationindicator, and it will be further seen that a combined rate andacceleration indicating system is provided without sacrice ofsimplicity.

The angular velocity and acceleration instrument provided by the presentinvention may be used for a wide variety of applications. It may be usedas a rate-of-turn indicating instrument for an aircraft, wherein thefork II is mounted with the axis 24 normally vertical, but for bestresults the natural frequency and tuning of the fork should be the samefor transverse as the torsional oscillations. It is useful, also, formaking scientific measurements, and for demonstrating physicalprinciples, as for example, for providing an indication of the earthsrotation.

It is not necessary for the purpose of the present invention that atuned fork II be employed as the device for periodic variation of momentof inertia. Any suitable arrangement `for periodically varying themoment of inertia of a mass may be employed for this purpose.

Moreover, it is not necessary for the present invention thatpiezoelectric crystal units be employed as vibration pickup devices. Anydevice suitable for producing an output signal varying according tomovement may be employed.

While the signal voltage produced by pickup device 23 is illustratedonly as employed to produce indications of angular velocity andacceleration, this voltage may be employed for a variety of other uses.For example, the reversible-phase alternating component of the output ofpickup unit 23 may be employed for control of a servo mechanism, eitherfor directly rotating the base I3 of the tuned fork assembly, or forautomatic vcontrol of a craft, the invention being used as 7 anorientation responsive device for craft stabilization.

Since many'changes could be made in the above construction and manylapparently widely different embodiments of this invention could be madewithout departing frpm the scope thereof,

weighted leaf spring elastically clamped at one end, so that it isforced to turn with the vehi- ,7. A rate of turn indicator comprising abase subject to being turned, a tuned fork having two tines .elasticallycoupled to said base adjacent the junction of said tines, means forvibrating said tines periodically and rapidly so as to vary the spacebetween the free ends of the same, and

means responsiveto variations in, thetwist bedetecting rotation of saidbase.

8. Orientation responsive apparatus comprising a base, a tuned forkhavingA two tines elastically connected to said base, means responsiveto vibration of said tines for applying vibration sustaining forces tosaidfork substantially 'at rescle abut an axis parallel to the springbut is freeonance therewith for periodically varying the at its weightedend to vibrate at its natural period about a transverse axis, means formaintaining such vibration, said spring also having a natural torsionalperiod equal to the aforesaidl vibrational period, and means fordetecting and measuring the amplitude and phase of said torsionalvibration as an indication of the rate and direction of turn of thevehicle.

2. A turn indicator for indicating 'orientation about an axis comprisinga'bse which orients about such axis, a movable' mass elastically coupledto said base with suiiicient stiiness to force' orientation of said masswith said base, but with sufficient resilience to permit a period ofoscillation, the elastici y of said mass also permitting free vibrationalternately toward and away from said orientation axis of the same lat anatural frequency the same as that of said torsional oscillation,andmeans for detecting and measuring the amplitude of the torsionaloscillations about said axis for indicating the rate of orientation.

3. A turn indicator for vehicles, comprising a base, a movable masselastically connected to said base, periodic means for vibrating saidmass substantially toward and away from an axis, means for detectingperiodic variations of relative angular displacement of said mass andsaid base about said axis for deriving a measure of angular velocity ofsaid base, and means for detecting variations of average vrelativeangular displacement of said mass and said base about said axis forderiving a measure of angular acceleration of the vehicle.

4. Apparatus responsive to changes of orientation comprising a base, aplurality of movable masses normally positioned symmetrically about anaxis therebetween,v motive means' for alternately drawing said massestoward said axis and repelling them from said axis, elastic torsionalvconstraining means connecting said masses to said base, and meansresponsive to variations of orientation of said masses and said baseabout said axis for detecting rotation of said base about said axis.

5. Apparatusasv defined in claim 4, further inl cluding means responsiveto the amplitude of movement of said masses for regulating said motivemeans to suppress changes of vibration amplitude of said masses.

6. Orientation responsive apparatus comprising a base, a fork having twotines elastically'interconnected, means for vibrating said tines alterlnately toward each other and apart from each nitural torsional spacingbetwen said tines, and means responcsive to relative twist of said forkand said base about an axis of symmetry of said tines producing asignalupon rotation' of said base.

means for vibrating said tines alternately toward `each other and apartfrom each other, elastic 'torsional constraining ,means connecting saidfork to said base -for permitting a relative angular positionalvariation between said fork and said baseaccording to variation oftorsion in said elastic means, and phase-sensitive detector meansresponsive to said relative angular positional variation for detectingthe amplitude and phase thereof relative to the phase of vibration ofsaid tines accompanying rotation of said base.

10. Apparatus as dened in claim 9 further including means responsive toa unidirectional componentof .relative angular positional variation`between said fork and said base for providing a measure of angularacceleration of said base.

11..A,rate of turn indicator comprising a base, a tuned fork` having twotines elastically connected to said base, means responsive to lmovementof said tines for applying to said fork vibration sustaining forcessubstantially in resonance therewith, means responsive to relative twistbetween said fork and. said base for providing an alternatingvoltagevarying with rotation of said base,v and phase-sensitive detectormeans responsive to movement of said tines for providing a measure ofthe amplitude and the phase of said alternating voltagerelative tothemovement of said tines.

--12. Apparatusresponsive to change of orientation, comprising a base, atuned fork having a plurality oi tines resiliently connected to saidbase, electromagnetic means for varying the spacing between saidvtinesin accordance with an applied voltage, vibration-iesponsive means forproducinga voltage varying according to the vibration of said tines,amplifier means responsive to the output of said vibration-responsivemeans and connected to said electromagnetic means for periodicallyvarying the spacingv between said tines at a frequency determined bythecharac- -teristics of said tuned fork, a phase-sensitive apparatus,means for supplying to said phase-sensitive apparatus a phase referencesignal derived from said vibration-responsive means, and meansresponsive to torsional vibrations between said tuned `fork and saidbase for delivering to said phase-sensitive apparatus an alternatingvoltage varying according to relative variations of position of saidfork and said base about the axis of said fork.

13. Apparatus as defined in lclaim 12, further including meansresponsive to an amplified version of the output of said'vibration-responsive means for varying the gain of said-amplier intweenthe junction of said tines and said base for 20 9.1App8gratus responsiveto change of orienta-` tion, comprising a base, a fork having two tines,

versely according to variations of strength of the vibration of saidfork, whereby variations of vibration amplitude of the tines of saidfork are suppressed.

14. A turn indicator for indicating the rate-ofturn of a craft about anaxis, comprising a. tuning fork-like structure mounted with its stemparallel to said axis, means for maintaining the vibration of saidtuning fork at a constant amplitude, a piezoelectric crystal pickupdevice connected to said stem in such manner that alternating stressesare applied thereto by the alternating variations in torsion in saidstem due to a turn, and a rateof -turn indicator actuated by thealternating output of said crystal.

15. A turn indicator as claimed in claim 14, wherein the frequency ofthe alternating output of said crystal is the same as the period oi' thetuning fork and the amplitude of the electromotive force varies with therate of turn.

JOSEPH LYMAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,728,904 Herr Sept. 17, 19292,231,439 Dudenhausen Feb. 11, 1941 2,266,449 Ullrich Dec. 16, 19412,309,853 Lyman Feb. 2, 1943 FOREIGN PATENTS Number A y Country Date289,862 Great Britain Aug. 6, 1929 692,497 Germany June 20, 1940

